1. Field of the Invention
The invention relates to backlighting systems used with liquid crystal displays, and more particularly to light pipe systems.
2. Description of the Related Art
Liquid crystal displays (LCD's) are commonly used in portable computer systems, televisions and other electronic devices. An LCD requires a source of light for operation because the LCD is effectively a light valve, allowing transmission of light in one state and blocking transmission of light in a second state. Backlighting the LCD has become the most popular source of light in personal computer systems because of the improved contrast ratios and brightnesses possible. Because conventional monochrome LCD's are only approximately 12% transmissive and color LCD's are only approximately 2% transmissive, relative large amounts of uniform light are necessary to provide a visible display. If power consumption and space were not of concern the necessary level and uniformity of backlight could be obtained.
However, in portable devices power consumption, which directly effects battery life, and space are major concerns. Thus there is a need to obtain a sufficiently uniform and bright backlight level with as little power as possible in as little space as possible at, of course, as low a cost as possible.
Numerous designs exist which trade off various of these goals to achieve a balanced display. Several of these designs, such as light curtains and light pipes, are shown in the figures and will be described in detail later. The designs generally trade off uniformity of backlighting for space or efficiency. The designs utilize various scattering means and a final diffuser before the light is presented to the LCD. The scattering means and the diffusers both allow loss of light and thus reduce the efficiency of the transfer from the light source to the LCD. While the designs are adequate in some cases, the demands for longer battery life with monochrome LCD's or equal battery life with color LCD's are present, as is a desire for the use of less space.